//
//  MealPlanSyncManager.swift
//  Nextcloud Cookbook iOS Client
//

import Foundation
import OSLog

@MainActor
class MealPlanSyncManager {
    private weak var appState: AppState?
    private weak var mealPlanManager: MealPlanManager?

    private var debounceTimers: [String: Task<Void, Never>] = [:]
    private let debounceInterval: TimeInterval = 2.0

    init(appState: AppState, mealPlanManager: MealPlanManager) {
        self.appState = appState
        self.mealPlanManager = mealPlanManager
    }

    // MARK: - Push Flow

    func scheduleSync(forRecipeId recipeId: String) {
        guard UserSettings.shared.mealPlanSyncEnabled else { return }

        debounceTimers[recipeId]?.cancel()
        debounceTimers[recipeId] = Task { [weak self] in
            try? await Task.sleep(nanoseconds: UInt64(2_000_000_000))
            guard !Task.isCancelled else { return }
            await self?.pushMealPlanState(forRecipeId: recipeId)
        }
    }

    func pushMealPlanState(forRecipeId recipeId: String) async {
        guard let appState, let mealPlanManager else { return }
        guard let recipeIdInt = Int(recipeId) else { return }

        let localAssignment = mealPlanManager.assignment(forRecipeId: recipeId)

        guard let serverRecipe = await appState.getRecipe(id: recipeIdInt, fetchMode: .onlyServer) else {
            Logger.data.error("Meal plan sync: failed to fetch recipe \(recipeId) from server")
            return
        }

        let merged = mergeAssignments(local: localAssignment, server: serverRecipe.mealPlanAssignment)

        var updatedRecipe = serverRecipe
        updatedRecipe.mealPlanAssignment = merged
        let (_, alert) = await appState.uploadRecipe(recipeDetail: updatedRecipe, createNew: false)
        if let alert {
            Logger.data.error("Meal plan sync: failed to push state for recipe \(recipeId): \(String(describing: alert))")
        }
    }

    // MARK: - Pull Flow

    func reconcileFromServer(serverAssignment: MealPlanAssignment?, recipeId: String, recipeName: String) {
        guard let mealPlanManager else { return }
        mealPlanManager.reconcileFromServer(serverAssignment: serverAssignment, recipeId: recipeId, recipeName: recipeName)
    }

    // MARK: - Initial Sync

    func performInitialSync() async {
        guard let appState, let mealPlanManager else { return }

        let recipeIds = Array(mealPlanManager.entriesByDate.values.flatMap { $0 }.map(\.recipeId))
        let uniqueIds = Array(Set(recipeIds))

        for recipeId in uniqueIds {
            guard let recipeIdInt = Int(recipeId) else { continue }

            await pushMealPlanState(forRecipeId: recipeId)

            if let serverRecipe = await appState.getRecipe(id: recipeIdInt, fetchMode: .onlyServer) {
                reconcileFromServer(
                    serverAssignment: serverRecipe.mealPlanAssignment,
                    recipeId: recipeId,
                    recipeName: serverRecipe.name
                )
            }
        }
    }

    // MARK: - Merge Logic

    private func mergeAssignments(local: MealPlanAssignment?, server: MealPlanAssignment?) -> MealPlanAssignment {
        guard let local else { return server ?? MealPlanAssignment() }
        guard let server else { return local }

        var merged = local.dates
        for (dayStr, serverEntry) in server.dates {
            if let localEntry = merged[dayStr] {
                let localDate = MealPlanDate.date(from: localEntry.modifiedAt) ?? .distantPast
                let serverDate = MealPlanDate.date(from: serverEntry.modifiedAt) ?? .distantPast
                if serverDate > localDate {
                    merged[dayStr] = serverEntry
                }
            } else {
                merged[dayStr] = serverEntry
            }
        }

        // Prune all date entries older than 30 days
        let cutoff = Calendar.current.date(byAdding: .day, value: -30, to: Calendar.current.startOfDay(for: Date()))!
        merged = merged.filter { dayStr, _ in
            guard let date = MealPlanDate.dateFromDay(dayStr) else { return true }
            return date >= cutoff
        }

        return MealPlanAssignment(
            lastModified: MealPlanDate.now(),
            dates: merged
        )
    }
}